In a known chuck of this kind (discourse by the firm Gottlieb Guhring KG, 7480 Sigmaringen, on the occasion of a meeting of the "Machine/Tool Interface" working party on 22.5.1987 in Frankfurt, at the Association of German Mechanical Engineering Institutes), the clamping jaws are designed as rockers, which is associated with certain drawbacks. When, during clamping, the second ends of the clamping jaws are forced outwards by the clamping cone, the hooked first ends of the clamping jaws are supported against the annular groove in the second machine part. But as the clamping jaws perform a tilting movement, there is only linear contact between the first ends and the groove flank against which they are supported. Similarly, the second ends abut against the groove flank of the attachment with linear contact. As a result of this linear contact, there is high contact pressure which is associated with correspondingly high wear. Furthermore the axial stroke which the second ends of the clamping jaws perform during their tilting movement is relatively small. Consequently, the cooperating machine parts may have only very low tolerances in an axial direction, in particular the groove flank in the attachment opposite the contact face thereof and the groove flank in the second machine part opposite the end face thereof. Also, the clamping jaws are subject to bending stress during their tilting movement and must accordingly have a correspondingly large cross-section. Consequently, the known chuck has larger structural dimensions in the radial direction and requires a correspondingly large diameter of the attachment on the first machine part.
It is therefore the object of the invention to provide a chuck for axially clamping two machine parts which are releasable from each other, in particular for clamping a tool portion in a tool holding fixture, of the kind mentioned hereinbefore, in which during the whole clamping process surface contact is constantly ensured between the cooperating surfaces of the clamping jaws and the groove flanks in both machine parts, which has smaller structural dimensions in a radial direction and in which greater tolerances are permissible for the cooperating machine parts in an axial direction.
According to the invention, this is achieved by the fact that in the region of the first ends of the clamping jaws, an additional clamping cone acting on these ends is provided at the clamping sleeve so that during axial movement of the clamping sleeve the clamping jaws are movable radially outwards or inwards parallel to themselves, and the clamping jaws comprise at both their ends clamping surfaces whose angular position relative to the central axis is adapted to the groove flanks, so that during the whole clamping process there is surface contact between the clamping surfaces and the groove flanks.
Due to the surface contact during the whole clamping process, there is a lower contact pressure and hence also less wear between the cooperating surfaces. At the same time, due to the lower contact pressure there is also greater rigidity. During the clamping process, the clamping jaws are displaced radially outwards parallel to themselves and no longer, as before, tilted. In this case, only a tensile stress and no bending stress is produced in the clamping jaws. The clamping jaws may consequently have a smaller cross-section, whereby the whole chuck can be built smaller in diameter. Moreover the cooperating machine parts can have greater tolerances in the axial direction. This is due to the fact that the clamping surfaces at the ends of the clamping jaws and the groove flanks during outward movement of the clamping jaws act as wedge surfaces and cause a correspondingly large axial movement between the machine parts. At the same time, greater axial contact pressures are caused between the contact face and the end face, and hence greater rigidity is obtained between the machine parts clamped together. The angles at which the clamping surfaces and the groove flanks are inclined to the bore axis or shaft axis can be varied, in order thus to change the ratio of the radial force exerted by the clamping jaws, to the axial force, and to adapt it to the respective conditions.
Further advantageous developments of the invention are characterised in the subsidiary claims.